Biotemplated inorganic materials

ABSTRACT

A method of making a metal oxide nanoparticle comprising contacting an aqueous solution of a metal salt with an oxidant. The method is safe, environmentally benign, and uses readily available precursors. The size of the nanoparticles, which can be as small as 1 nm or smaller, can be controlled by selecting appropriate conditions. The method is compatible with biologically derived scaffolds, such as virus particles chosen to bind a desired material. The resulting nanoparticles can be porous and provide advantageous properties as a catalyst.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. patent application Ser. No.12/911,340, filed Oct. 25, 2010, which claims priority to provisionalU.S. Patent Application No. 61/254,473, filed Oct. 23, 2009, which areincorporated by reference in their entirety.

FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with government support under Grant No.DAAD19-03-D-0004 awarded by the Army Research Office. The government hascertain rights in the invention.

TECHNICAL FIELD

This invention relates to biotemplated inorganic materials.

BACKGROUND

Hydrogen is a useful energy source in fuel cells and batteries. Becauseit is difficult to obtain hydrogen from a gas source, it can bedesirable to obtain it from a liquid source. Liquid fuels can alsoprovide higher energy densities than gaseous fuels. A catalyst may beused to obtain hydrogen from a liquid source such as ethanol. Catalystsshould be relatively inexpensive, highly active and stable. Efficiencyand stability of catalysts are affected by surface area, physicalisolation and fixation of metals, the presence of active materials nearthe surface of the 3-D structure, and sintering stability, among otherfactors.

SUMMARY

Metal oxides represent a very large class of materials useful in avariety of applications including electronics, optics, ceramics, andcatalysts. Many applications that are dependent upon the surface area ofthe material or size of the crystallite domain can be further enhancedthrough the use of the nanoparticle form of metal oxides. As such, metaloxide nanoparticles have garnered much research interest over the pastfew decades, both in novel applications and new synthesis methods.

In general, size control is desirable in nanoparticle synthesis, andsmall, monodisperse nanoparticles can be especially useful. Reactionconditions are preferably safe and environmentally friendly (e.g.,limiting the quantity of organic solvents and hazard reagents), usereadily available and inexpensive starting materials, and can prepare avariety of materials under similar reaction conditions.

The efficiency of catalytic materials is influenced by both the chemicalnature of the material, and its physical form. For example, inheterogeneous catalysis (e.g., where a solid phase catalysis is exposedto gas and/or liquid phase reactants), a high specific surface can bepreferred. Thermal stability is desirable as well.

In one aspect, a catalytic material suitable for high-temperatureheterogeneous catalysis includes nanoporous metal oxide nanoparticles.The nanoporous metal oxide nanoparticles can include a nanostructure.The nanostructure can further include a transition metal.

The metal oxide can include a manganese oxide, a magnesium oxide, analuminum oxide, a silicon oxide, a zinc oxide, a copper oxide, a nickeloxide, a cobalt oxide, an iron oxide, a titanium oxide, yttrium oxide, azirconium oxide, a niobium oxide, a ruthenium oxide, a rhodium oxide, apalladium oxide, a silver oxide, an indium oxide, a tin oxide, anlanthanum oxide, an iridium oxide, a platinum oxide, a gold oxide, acerium oxide, a neodymium oxide, a praseodymium oxide, an erbium oxide,a dysprosium oxide, a terbium oxide, a samarium oxide, a lutetium oxide,a gadolinium oxide, a ytterbium oxide, a europium oxide, a holmiumoxide, a scandium oxide, or a combination thereof. In one embodiment,the nanoporous metal oxide nanoparticles include ceria.

A measured X-ray diffraction pattern of the nanoporous metal oxidenanoparticles can be substantially unchanged after 60 hours at 400° C.The nanoporous metal oxide nanoparticles can have a BET surface area ofgreater than 150 m²/g. The nanoporous metal oxide nanoparticles can besubstantially free of pores having a width greater than 20 nm.

In another aspect, a method of producing a metal oxide nanoparticleincludes contacting an aqueous solution of a metal salt with an oxidant.The oxidant can include hydrogen peroxide. The aqueous solution caninclude two or more different metal salts. The method can includeselecting nanoparticle-forming conditions to form nanoparticles having apredetermined size. The predetermined size can be in the range of 0.5 nmto 250 nm, for example, in the range of 1 nm to 100 nm.

The method can include forming a nanoparticle including a mixed metaloxide having the formula M¹ _(x)M² _((1−x))O_(y), wherein M¹ is a firstmetal, M² is a second metal, x represents the mole fraction of M¹ oftotal metal in the metal oxide, and y is such that the bulk metal oxideis charge-neutral. The mixed metal oxide can include oxygen vacancies.

The aqueous solution can include a virus particle having an affinity foran oxide of the metal in the aqueous solution. The virus particle can bean M13 bacteriophage.

In another aspect, a method of making supported catalytic materialincludes contacting a ceramic support with a virus particle to form asupported virus conjugate, the virus particle having a first surfacemoiety having affinity for the ceramic support and a second surfacemoiety having an affinity for a catalytic material; and forming aplurality of catalyst nanoparticles at the surface of the virusparticle.

The ceramic support can include silica, α-alumina, β-alumina, γ-alumina,rutile titania, austentite titania, ceria, zirconia, manganese oxide,manganese phosphate, manganese carbonate, zinc oxide, or a combinationthereof. Forming the plurality of catalyst nanoparticles can includecontacting the supported virus conjugate an aqueous solution of a metalsalt with an oxidant. The oxidant can include hydrogen peroxide. Theaqueous solution can include two or more different metal salts.

The method can include selecting nanoparticle-forming conditions to formnanoparticles having a predetermined size. The predetermined size is inthe range of 0.5 nm to 250 nm, for example, in the range of 1 nm to 100nm.

The method can include forming a nanoparticle including a mixed metaloxide having the formula M¹ _(x)M² _((1−x))O_(y), wherein M¹ is a firstmetal, M² is a second metal, x represents the mole fraction of M¹ oftotal metal in the metal oxide, and y is such that the bulk metal oxideis charge-neutral. The mixed metal oxide can include oxygen vacancies.

The details of one or more embodiments are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description and drawings, and fromthe claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic depiction of a viral-templated catalyst.

FIG. 2A is a TEM image of CeO₂ nanoparticles produced in the absence ofphage particles.

FIG. 2B is a TEM image of a CeO₂ nanoparticles produced in the presenceof phage particles.

FIG. 3 is a graph illustrating the coarsening behavior at 500° C. ofnanoparticles compared to nanowires templated with phage.

FIGS. 4A-B are graphs illustrating the pore size distribution of CeO₂nanoparticles prepared under different conditions.

FIG. 5 is an XRD measurement of 5% Ni-1% Rh on CeO₂ nanowires after 60hours of heat treatment at 400° C.

FIG. 6 is a schematic depiction of a test reactor to monitor catalysis.

FIGS. 7A-7B are graphs depicting the composition of gases produced in acatalytic reactor under varying conditions.

FIG. 8 is a schematic depiction of a virus-templated, supportedmaterial.

FIGS. 9A-9C are graphs depicting product output of different catalystsystems over time. FIGS. 9D-9E are X-ray diffraction patterns ofdifferent catalyst systems after use.

DETAILED DESCRIPTION

Catalysts for producing hydrogen, such as transition metal and/or noblemetal catalysts, can be prepared by a number of methods. Frequently, thecatalyst materials include catalyst particles (e.g., transition metaland/or noble metal particles) and a support. Flame hydrolysis involveshydrolyzing a metal chloride precursor, such as silicon tetrachloride,in a hydrogen/oxygen flame. The hydrogen burns and reacts with oxygen,producing very finely dispersed water molecules in the vapor phase,which then react with the metal chloride to form the corresponding metaloxide nanoparticle and hydrochloric acid. This method is often limitedby the availability of a precursor which decomposes upon contact withwater.

Another method of catalysis preparation is aerogel synthesis. An aerogelis formed when a liquid solvent in a solid-liquid mixture becomessupercritical and then changes phase to a vapor, exchanging with theenvironment without any rapid volume changes which might damage themicrostructure of the catalyst support. The remaining solid maintains ahigh level of network connectivity without collapsing and is desirablefor its high surface area and porosity.

A mesoporous material may be more interesting as a catalyst than a solidmaterial. Organic functionalization during particle formation canproduce the desired pore distribution. The initial particles are formedwith organic molecules such as tetraethoxysilane (TEOS) embedded intothe structure at room temperature. Subsequent heat treatments drive offthe organic molecules, leaving a solid with pores in it defined by themissing organic molecules. A micelle can also be used in this method ofcatalyst preparation.

Colloidal syntheses are broadly described as syntheses wherein a solidis precipitated from a solvent-soluble precursor into asolvent-insoluble solid nanoparticle mixture. Metallic clusters areformed by reducing metal ions in solution with an agent such as hydrogenor sodium borohydride. The reduced metal ions become zero-valent, losingtheir electrostatic repulsion, and are able to nucleate nanoparticles ofthe neutral metallic material. Colloidal syntheses are related to othermethods such as the usage of microemulsions, metal complexdecomposition, gas phase synthesis, high-gravity reactive precipitationand electrochemical synthesis.

Microwave-assisted synthesis depends on the ability of the material tochange local charge configuration and lose energy when this happens.This sort of synthesis can include the production of nanolayer carbideand nitrides on the surface of metal catalysts or the fluidization ofmetal along with carbon black in argon.

A catalyst can also be synthesized by dendrimer-metal precursor methods.A dendrimer can perform as a nanoreactor, allowing the polymer to growin a tree-like fashion. The steric hindrance of adjacent chainseventually cause the dendrimer to fold back on itself into a singlemolecule, where the inside of the dendrimer sphere can be made toattract metal ions in solution. Reduction of the metal-dendrimer complexcauses the complex to collapse, forming a nanoparticle inside thedendrimer. The entire dendrimer-metal nanocomposite is deposited onto aporous support and the dendrimer is then removed by either heattreatment of chemical means.

The catalyst particle distribution on a support has significant impacton the final properties of the catalyst. Incipient wetness impregnationor dry impregnation can be used to control the catalyst distribution.Adding an amount of solvent very close to the total pore volume of thesupport allows all of the solvent to be rapidly taken up into thesupport. Soaking in the precursor that is dissolved in the same solventresults in a diffusion-limited spread of catalyst material into thesupport, which causes the catalyst particles to be primarily located atthe surface of the support. Drying is also a major influence in thecatalyst particle distribution, wherein a constant drying rate resultsin most of the dissolved precursor forming catalyst species on theexternal surface of the support. In a second stage called the “firstfalling-rate period” the rate of drying steadily decreases in a roughlylinear fashion, resulting in the dissolved catalyst depositing internalto the support. The “second falling-rate period” where the drying ratefalls more gradually until the moisture content is eventually zero, thecatalyst particles are deposited at the center of the support.

Ceria (CeO₂) is a ceramic with excellent redox properties, and is acommon catalyst support used in a variety of reactions. In particular,ceria supported noble metals promote the production of hydrogen fromethanol. Specifically, this reaction is given byC₂H₅OH+2H₂O+1/2 O₂→2CO₂+5H₂See, for example, G. A. Deluga, J. R. Salge, L. D. S. Science 2004, 303,993, which is incorporated by reference in its entirety.

The activity of CeO₂ in assisting catalysis is heavily dependent uponthe type, size and distribution of oxygen vacancies in the CeO₂ fluoritecrystal structure. The vacancies can help in the efficiency forreversible oxygen release, which can allow for the formation of morestable states of catalytically active metals adsorbed to the surface.See, for example, F. Esch, S. Fabris, L. Z. Science 2005, 309, 752; andA. Trovarelli, Ed.; Catalysis by Ceria and Related Materials; ImperialCollege Press: 2002, each of which is incorporated by reference in itsentirety. Much work has been focused on what material is used inconjunction with CeO₂ in an effort to eliminate CO and acetaldehydebyproducts, increase efficiency, and decrease operating temperature ofthe reaction in addition to improving the properties of the CeO₂co-catalyst to enhance catalysis and simplify synthesis. See, forexample, J. Kugai, V. Subramani, C. S. Journal of Catalysis 2006, 238,430-440; S. Deshpande, S. Patil, S. K. Applied Physics Letters 2005, 87,133113; F. Zhang, P. Wang, J. K. Surface Science 2004, 563, 74-82; J. R.Salge, G. A. Deluga, L. D. S. Journal of Catalysis 2005, 235, 69-78; C.Zerva, C. J. P. Applied Catalysis B: Environmental 2006, 67, 105-112; H.Idriss, Platinum Metals Rev 2004, 48, 105-115; P.-Y. Sheng, A. Yee, G.A. B. Journal of Catalysis 2002, 208, 393-403; S. J. Morrison, P. Y.Sheng, A. Y. Prepr. Pap.-Am. Chem. Soc., Div. Petr. Chem. 2006, 51, 26;J. Kugai, S. Velu, C. S. Catalysis Letters 2005, 101, 255; M. Fuchs, B.Jenewein, S. P. Applied Catalysis A: General 2005, 294, 279-289; Y.Hirta, A. Harada, X. W. Ceramics International 2005, 31, 1007-1013; P.Dutta, S. Pal, M. S. S. American Chemical Society 2006; M. Romeo, K.Bak, J. E. F. Surface and Interface Analysis 1992, 20, 508-512; D. R.Mullins, S. H. Overbury, D. R. H. Surface Science 1998, 409, 307-319; T.Masui, K. Fujiware, K. M. Chem. Mater. 1997, 9, 2197-2204; M. Hirano, E.K. J. Am. Ceram. Soc. 1996, 79, 777-780; X. Yu, F. Li, X. Y. J. Am.Ceram. Soc. 1999, 83, 964; P. Chen, I. C. J. Am. Ceram. Soc. 1992, 76,1577-1583; T. Sato, T. Katakura, S. Y. Solid State Ionics 2004, 172,377-382; A. S. Bodke, S. S. Bharadwaj, L. D. S. Journal of Catalysis1998, 179, 138-149; and M. Yamashita, S. Yoshida, Y. F. Journal ofMaterials Science 2001, 37, 683-687, each of which is incorporated byreference in its entirety.

A bimetallic Ni—Rh/CeO₂ catalyst can produce less CO and cost less thana similar Rh/CeO₂ catalyst. Nickel is a less expensive metal and has ad-orbital very similar in shape to that of rhodium. Therefore, it canfacilitate similar reactions, while producing less acetaldehyde than Pt,Pd, Ru or Au. See, for example, J. Kugai, V. Subramani, C. S. Journal ofCatalysis 2006, 238, 430-440; and J. Kugai, S. Velu, C. S. CatalysisLetters 2005, 101, 255, each of which is incorporated by reference inits entirety. Kugai found that for reactions taking place around 375°C., nickel itself only achieved 40% conversion of ethanol while 10% Niand 1% Rh achieved over 92% conversion. Rhodium can improve catalystperformance. See, for example, J. Kugai, V. Subramani, C. S. Journal ofCatalysis 2006, 238, 430-440; and J. Kugai, S. Velu, C. S. CatalysisLetters 2005, 101, 255, each of which is incorporated by reference inits entirety.

Synthesis for CeO₂ nanocrystals can by accomplished in a variety ofways, such as solid-state reactions, hydrothermal syntheses, homogenousprecipitation or two-phase syntheses. See, for example, T. Masui, K.Fujiware, K. M. Chem. Mater. 1997, 9, 2197-2204; M. Hirano, E. K. J. Am.Ceram. Soc. 1996, 79, 777-780; X. Yu, F. Li, X. Y. J. Am. Ceram. Soc.1999, 83, 964; P. Chen, I. C. J. Am. Ceram. Soc. 1992, 76, 1577-1583; T.Sato, T. Katakura, S. Y. Solid State Ionics 2004, 172, 377-382; and M.Yamashita, S. Yoshida, Y. F. Journal of Materials Science 2001, 37,683-687, each of which is incorporated by reference in its entirety. Themost common commercial method of CeO₂ nanocrystal synthesis is wetimpregnation, where an existing CeO₂ foam is impregnated with rhodiumprecursors and calcined to produce nanoparticles attached to the CeO₂surface. Another method of nanoparticle synthesis is a biocompatiblesynthesis based on homogeneous precipitation. See, for example, T. Sato,T. Katakura, S. Y. Solid State Ionics 2004, 172, 377-382; and M.Yamashita, S. Yoshida, Y. F. Journal of Materials Science 2001, 37,683-687, each of which is incorporated by reference in its entirety.

A wide variety of metal oxide nanoparticles can be synthesized fromaqueous solution using hydrogen peroxide as an etchant to preventparticle growth during hydrolysis under basic conditions. The startingmaterials can include a metal salt, e.g., a metal chloride or metalnitrate. Increased amounts of hydrogen peroxide can decrease particlesize. In many cases, the metal oxide was formed immediately with ananocrystallite size ranging from 1 nm to several tens of nanometers.After synthesis, the particles were dried and heat treated toinvestigate phase changes and particle growth after calcination.

The reaction produces high quality nanoparticles using hydrogen peroxideconcentrations higher than reported in M. Yamashita, S. Yoshida, Y. F.Journal of Materials Science 2001, 37, 683-687, which is incorporated byreference in its entirety. For example, the mole ratio of H₂O₂ to metalcan be, for example, in the range of 0.001 to 100, in the range of 0.01to 10, or in the range of 0.1 to 10.

A mixed metal oxide can have the formula M¹ _(i)M² _(j)O_(x). M¹ and M²can each independently be a metal, or in some cases, a semi-metal suchas silicon. For example, M¹ and M² can each independently be magnesium,aluminum, silicon, scandium, titanium, manganese, iron, cobalt, nickel,copper, zinc, yttrium, zirconium, niobium, ruthenium, rhodium,palladium, silver, indium, tin, lanthanum, cerium, praseodymium,neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium,erbium, ytterbium, lutetium, iridium, platinum, gold, or another metal.

In general, the values of i, j, and x are non-negative. In someinstances, the value of i, j, or x can be an integer. In some cases, thesum of i and j can be an integer, and the sum of x and y can be aninteger. For example, a mixed metal oxide can have the formula M¹ _(i)M²_(1−i)O. In this formula, the sum of i and j is 1, and the value of x is1.

The metal oxide can include, but is not limited to, a manganese oxide(e.g., MnO_(x)), a magnesium oxide (e.g., MgO), an aluminum oxide (e.g.,Al₂O₃), a silicon oxide (e.g., SiO_(x)), a zinc oxide (e.g., ZnO), acopper oxide (e.g., CuO or Cu/CuO), a nickel oxide (e.g., NiO orNi/NiO), a cobalt oxide (e.g., Co₃O₄ or Co/Co₃O₄), an iron oxide (e.g.,Fe₂O₃ as hematite or maghemite, or Fe₃O₄ as magnetite), a titaniumoxide, yttrium oxide, a zirconium oxide, a niobium oxide, a rutheniumoxide, a rhodium oxide, a palladium oxide, a silver oxide, an indiumoxide, a tin oxide, an lanthanum oxide, an iridium oxide, a platinumoxide, a gold oxide, a cerium oxide, a neodymium oxide, a praseodymiumoxide, an erbium oxide, a dysprosium oxide, a terbium oxide, a samariumoxide, a lutetium oxide, a gadolinium oxide, a ytterbium oxide, aeuropium oxide, a holmium oxide, a scandium oxide, or a combinationthereof.

The nanostructure of the Ni—Rh/CeO₂ system can have a substantial effecton the final product quality. Preferably, the nanostructure of thecatalyst has rhodium atoms (e.g., a majority of all rhodium atoms) neara CeO₂ oxygen vacancy, rhodium atoms at the surface of the structure(and therefore accessible to reactants), a high surface area/volumeratio; and rhodium atoms physically isolated from other rhodium atoms.These structural features can enhance the specific activity of thecatalyst. See, for example, J. R. Salge, G. A. Deluga, L. D. S. Journalof Catalysis 2005, 235, 69-78, which is incorporated by reference in itsentirety.

M13 bacteriophage can serve as a template for nanoparticle growth. See,for example, Ki Tae Nam, Dong-Wan Kim, P. J. Y. Science 2006, 312, 885,which is incorporated by reference in its entirety. Protein engineeringtechniques (e.g., phage display) can produce a virus that has a proteincoat with binding affinity for a desired target material, e.g., aninorganic material such as a metal or a metal oxide. The protein coatprotein can have a metal binding motif, which, for example, can be anegatively charged motif, e.g., tetraglutamate or a peptide with abinding affinity to a metal. For example, the motif can be a 12-aminoacid peptide with a high affinity for Au. In one example, engineered M13virus particles allowed control of the assembly of nanowires of Co₃O₄with a small percentage of Au dopant. Id.

While M13 bacteriophage can have a major coat protein with a motif thatbinds specific metals, the motif can also block binding of other metals.For example, tetraglutamate can interact with various metal ions butblocks interaction with Au due to electrostatic repulsion. See, forexample, Ki Tae Nam, Dong-Wan Kim, P. J. Y. Science 2006, 312, 885,which is incorporated by reference in its entirety. M13 bacteriophagewith a major coat protein specific to CeO₂ and a small percentage ofpeptides specific for rhodium alone can serve as a template for CeO₂nanowire can be created with a spatially interspersed rhodiumnanocrystals. FIG. 1 depicts a nanostructure exhibiting desirableproperties. The virus with randomly expressed proteins capable ofnucleating either CeO₂ or rhodium metal are grown first, and thensubsequently exposed to precursors of CeO₂ and rhodium to produce aprotein templated catalyst.

The nanostructured system increases the fraction of rhodium atoms thatare touching a Ce atom, increasing the probability that a rhodium —CeO₂vacancy will occur and reducing the amount of inactive rhodium. They canreduce the amount of rhodium that is required for the system, therebydecreasing cost. Next, the M13 bacteriophage acts as a scaffold with athin layer (e.g., a monolayer) of nanocrystals at the surface, allowingthe majority of rhodium atoms to be near the surface and a very smallamount of rhodium atoms to be trapped. This can further reduce theamount of rhodium needed for the system since the inactive rhodium isdecreased. Third, the resultant nanorod can have a high surface area tovolume ratio. The final pore size distribution may also have asubstantial impact on the final product distribution and catalystactivity. Finally, the random locations of the metal-binding motifs onthe M13 viral coat can favor physical separation of adjacent rhodiumnanocrystals compared to that given by wet impregnation orco-precipitation. When physically separated, rhodium nanocrystals areunlikely to sinter together due to hotspots during catalysis. Thephysical separation can be enhanced by the 1-D nature of a nanowire.

In general, smaller ceria nanoparticles can be preferable, due to theirhigh surface area to volume ratio and oxygen vacancy concentration. Theoxygen vacancy concentration coupled with the inherently high oxygendiffusion rate in the fluorite structure of ceria creates an excellentsurface for absorbing and releasing oxygen as needed to support redoxcatalysts. See J. Kugai, V. Subramani, C. S. Journal of Catalysis 2006,238, 430-440; S. Deshpande, S. Patil, S. K. Applied Physics Letters2005, 87, 133113; F. Zhang, P. Wang, J. K. Surface Science 2004, 563,74-82. C. Zerva, C. J. P. Applied Catalysis B: Environmental 2006, 67,105-112; F. Esch, S. Fabris, L. Z. Science 2005, 309, 752; A.Trovarelli, Ed.; Catalysis by Ceria and Related Materials; ImperialCollege Press: 2002; Q. Fu, H. Saltsburg, M. F.-S. Science 2003, 301,935; and Z. Liu, S. Jenkins, D. K. Physical Review Letters 2005, 94,196102, each of which is incorporated by reference in its entirety.Smaller particles can have a higher activation energy to sintering whichexplains why it appears to have a large temperature response, suggestingthat for different operating temperatures, different initial sizednanoparticles can provide a high long-term stability. Forming thenanowires with a thin coat can limit the sintering to occur in twodimensions. This can result in resistance to particle coarsening, whichin most systems, can cause a gradual degradation of the catalyst.

M13 bacteriophage can be engineered to bind to different materials atdifferent sites, by introducing different affinity motifs in the majorand minor coat proteins. FIG. 8 illustrates a composite material 10include a ceramic support 20. Bacteriophage particles 30 are bound tothe surface of support 20 by coat proteins 40 selected to have affinityfor ceramic material of support 20. Catalytic metal oxide nanoparticles50 are bound to virus particles 30 by coat proteins selected to haveaffinity for the metal oxide. Composite material 10 provides a largequantity (e.g., a high surface area) of catalytic metal oxidenanoparticles 50. Because the nanoparticles are bound to support 20, thecomposite material can be handled more conveniently, for example inpreparing a catalytic reactor.

Example 1

Previously, an E4 strain of M13 phage that expresses four glutamic acids(EEEE) on the surface of the major coat was developed. See, for example,Ki Tae Nam, Dong-Wan Kim, P. J. Y. Science 2006, 312, 885, which isincorporated by reference in its entirety. The E4 strain typicallymutates to an E3 strain which includes AEEE instead of EEEE after a fewamplications. To form CeO₂ nanowires on an E3 phage, the E3 phage with ametal-binding motif on a coat protein is amplified to a concentration of˜10¹⁴ mL⁻¹. 500 μL of CeCl₃ was incubated for 10 minutes with 100 μL ofthe E3 phage with between 10⁵ and 10¹² total phage particles added fromthe amplified solution. 50 μL of NaOH simultaneously with 1 μL 0.3 wt %H₂O₂ was added to the mixture and immediately vortexed. The resultantnanowires were put on a TEM grid for imaging. FIG. 2A shows a TEM imageof the system with no virus. FIG. 2B shows a TEM image of CeO₂ nanowiresproduced with 10¹² phage particles in solution. In several places, thephage can be identified by the thin hollow while line (indicated byarrows) showing the core of the phage where no CeO₂ is present.

The addition of phage to the CeO₂ synthesis resulted in highly enhancedthermal stability wherein the nanowires of CeO₂ have essentiallyidentical nanocrystallinity before and after 60 hours of heat treatmentat 400° C. FIG. 3 shows the difference in coarsening behavior, asmeasured by X-ray diffraction, at 500° C. sintering conditions betweennanoparticles and nanowires templated with phage as a function of phageconcentration. The addition of phage also suppresses growth from the8^(th) order behavior seen in nanoparticles alone to growth ordershigher than 20 in 500° C. sintering conditions.

Example 2

Rh—Ni/CeO₂ nanoparticles were formed by co-precipitating RhCl₃, NiCl₂and CeCl₃ using NaOH and H₂O₂ as pH modifier and oxidizer, respectively,to form Rh₂O₃, NiO and CeO₂, which are the catalytically active phasesof each material. A solution containing 1% RhCl₃, 5% NiCl₂ and 94% CeCl₃(percent of total metal ions) was made and precipitated by adding NaOHand H₂O₂ in the same way as was done for the CeO₂ nanoparticles inExample 1, at a 10× H₂O₂ concentration (i.e., 10-fold more concentratedthan reported in Yamashita and Yoshita). The solution was dried in theair and then heat treated at 200° C. Nanoparticles of Rh₂O₃ were formedafter heat treatment at 400° C. The nanoparticles were approximately 4.0nm and were black. Similarly, nanoparticles of NiO were formed afterheat treatment at 400° C. The nanoparticles were approximately 9.6 nmand went from a bluish-green powder to a dark black after heattreatment.

To verify that the ratio of metal atoms in the final particles wasroughly the same as the ratio of the precursor mixture, TEM images of afinal dried nanoparticle sample made with 5% RhCl₃ and 95% CeCl₃ wererecorded. Energy dispersive spectroscopy showed that 88% Ce, 5% Rh, and7% Cl, which is approximately in line with the input precursors. Thenanoparticle powder had an average crystalline diameter of about 3.0 nmas measured by X-ray diffraction, and a BET surface area of 152 m²/gwith a pore volume of 0.113 cm³/g.

Nanowires were then formed by simple co-precipitation by using asolution with 1% RhCl₃, 5% NiCl₂ and 94% CeCl₃. E3 phage was added toget an concentration of 10¹¹ phage particles per mL with 100 mM totalconcentration of metal salt precursors. The resulting nanowire powderhad an average crystallite size of 3.5 nm, and a BET surface area of 180m²/g with a pore volume of 0.121 cm³/g. FIG. 4A shows the poredistribution calculated using a density functional theory model of theCeO₂ nanoparticles formed in the absence of virus particles. FIG. 4Bshow the pore distribution the CeO₂ nanowires formed by co-precipitationwith E3. The nanowire powder had an average crystalline size of 3.5 nm,and a BET surface area of 180 m²/g with a pore volume of 0.121 cm³/g.The nanoparticles have less total area contained in the pores while thenanowires also have a narrower pore size.

FIG. 5 shows that after the nanowire powder was heat treated at 400° C.for 60 hours, the average change in nanocrystal size was less than 0.3nm and no precipitation of minor phases was observed. In thenanoparticle sample, however, there was precipitation. This suggestsgood integration of rhodium and nickel into the nanowire structure, asopposed to discrete clusters of rhodium and nickel separate from thenanowires.

The nanowires and nanoparticles were then tested for catalytic activityin converting ethanol to hydrogen and CO₂. FIG. 6 shows a schematicoverview of the test reactor. After the system was calibrated withwater, ethanol, and different gases, air was flowed through the FTIRsystem 10 without ethanol or water being injected into the manifold 7 ateach temperature. Then, the liquid water tank 2 with flow controller 4and liquid ethanol tank 3 with flow controller 5 allowed water andethanol, respectively to be heated in heating manifold 7. Gascalibrations were also done with gas flow controller 6. All tubing 9 is316 stainless steel and in most places wrapped with heat rope and layersof insulation to prevent condensation of water inside the tubing. Thecatalyst powders were heated from the outside by use of tube furnace 8.The powders were held on a filter in tube furnace 8. A set of dualminiature solenoid valves 11 were allowed to sample the output streamafter passing though the FTIR. Hydrogen sensor 12 is attached to acomputer for measurements. Finally, CO₂, CH₄, CO, CH₃COH and H₂concentrations were calculated and normalized so that they sum 100% toaccount for fluctuations in water concentrations.

FIGS. 7A and 7B provide a comparison of gas output composition as afunction of temperature for co-precipitated nanoparticles (FIG. 7A) andfor nanowires templated on E3 (FIG. 7B). Total flow rate was 10.882mmol/min, and the amount of catalyst in both cases was 500 mg (˜2.905mmol assuming CeO₂), for a GHSV of 32.7 hr⁻¹.

Example 3

Ni—Rh@CeO2 was formed by using the oxidation and hydrolysis of CeCl₃with RhCl₃ and NiCl₂ in aqueous solution. Water (120 mL) was either usedas-is or by diluting E3M13 phage (AEEE expressed on the pVIII major coatprotein) to a concentration of approximately 10¹²/mL by adding ˜10-100μL of phage solution at a spectroscopically measured approximateconcentration of ˜10¹⁵/mL. The diluted phage or phage-free water wasmixed for 30 min in a 500 mL Ehrlenmyer flask at room temperature toensure good dispersion. For comparison of different phageconcentrations, the concentrated phage was decreased in concentrationserially by factors of 10 to achieve an internally accurate phage ratio.

After mixing, 30 mL of 1 M metal chloride solution containing RhCl₃(anhydrous, 99.9% Alfa Aesar), NiCl₂ (anhydrous, 98% Alfa Aesar), andCeCl₃ (heptahydrate, 99% Acros Organics) in a 1:10:89 molar ratio(RhCl₃/NiCl₂/CeCl₃) was added to either diluted M13 phage or phage-freewater and allowed to equilibrate over 30 min at room temperature at 650rpm.

After equilibration, nanoparticles were nucleated by the rapid additionof a mixture of 30 mL of 3 M NaOH (99%, Mallinckrodt Chemicals) and 60μL of 30 wt % H₂O₂ (29.0-32.0% Reagent ACS, VWR). Immediately afteraddition, the solution turned dark brown-red and solids formed with gasevolution. The solution was stirred at 650 rpm for 30 min to allow thereaction to go to completion. After completion, the suspension wasprecipitated using centrifugation and the supernatant discarded. Theprecipitate was redissolved in water to wash residual NaCl and NaOH fromthe powder and recentrifuged for a total of three washings. Afterwashing, the precipitate was set out at room temperature in a Petri dishin air until dry. After drying, the powders were finely ground and heattreated at 400° C. for 2 h until the final powder was produced. TGA onsimilar samples show that 350° C. was a sufficiently high temperature toremove nearly all of the carbon from the sample.

Catalyst powders were loaded in an unpacked layer in a 316 stainlesssteel chamber (Swagelok Part SS-4F-05 In-Line Particulate Filter) wherethe filter element was replaced with a 12 mm fine porosity frittedborosilicate disk (ChemGlass Part CG-201-05) to a typical depth of ˜5 mmin the case of 1000 mg samples. In the case of very small samples (100mg), a thin layer was placed on the borosilicate disk by gently tappingthe catalyst chamber until the disk was no longer visible. The disk wasreplaced after each test, and the gas hourly space velocity (GHSV) waschanged by using varying amounts of catalyst powder while keeping theabsolute flow rate constant to eliminate variations due to reactoractivity or pressure changes due to increased flow rate. The GHSV wasestimated by using an assumed catalyst density of 1 g/mL, and the gasvolume was converted to a standard volume at 298 K and 1 atm.

The entire catalyst chamber was heated to the desired reactiontemperature using a tube furnace (HTF55122A 1-Zone 1200° C. furnace withCC58114COMA-1 Digital Controller, Thermo Fisher Scientific). Thepreheating chamber was made out of 1 in. diameter 316 stainless steeltubing with custom machined Swagelok fittings to allow for the fuelinjector (16 lb/h disc high-Z fuel injector, Racetronix Model 621040) toinject liquid directly into the preheating chamber. The fuel injectortemperature was measured using a thermocouple on the Swagelok fittingand heated with heat tape (McMASTERCARR Part 4550T12) wrapped around thepreheating chamber outside of the furnace controlled using a temperaturecontroller (Omega CNI3233-C24) to 120° C.

The air mass flow controller in all experiments was set at 14 mL/min(2.94 mL/min O₂), argon flow controller was set at approximately 100mL/min, and ethanol was injected with the fuel injector using a 1.157 mspulse every 2 s at 50 psi and 24 VDC. This pulse length was equivalentto 2.91 μL per pulse based on fuel injector calibrations done byinjecting known pulse lengths and counting the number of pulses requiredto inject 10 mL of liquid. The total molar ratio at STP for theseamounts is 1.7:1:10:11 (air/EtOH/water/argon) with a total flow rate ofroughly 200 mL/min.

The internal temperature of the preheating chamber was monitored using atemperature probe placed just above the catalyst bed with a temperaturecontroller (Omega CNI3233-C24), and the temperature of the input gas wastypically close to the temperature of the furnace. The preheatingchamber had two ⅛ in. Swagelok fittings to allow for argon and air to beadded to the mixture using a mass flow controller (Alicat MC-1 SLPM-D/5M 0-1 SLPM) for the air and a manual flow controller for the argonbackflow gas.

Below the reactor bed, the gas mixture was allowed to equilibrate in a150 mL double-ended 316 stainless steel sample cylinder (Swagelok Part316 L-50DF4-150) placed inside the furnace to prevent condensation. Thisvolume represents a time to equilibration of roughly 7.5 min assumingapproximately 10 times the replacement time to fully equilibrate at anew composition. The output gas was carried through a 0.5 μm 316stainless steel filter (Swagelok Part SS-4FWS-05) to the GC via ⅛ in.316 stainless steel tubing sheathed in ¼ in. copper tubing wrapped withhigh-temperature heat rope (McMASTERCARR Part 3641K26) and using atemperature controller (Omega CNI3233-C24) set to 120° C. to preventcondensation. The tubing entered the GC through a valve with a 250 μLsample loop held at 150° C. after passing through another 0.5 μm 316stainless steel filter (Swagelok Part SS-2F-05) to prevent clogs in theGC valves. The equilibrated composition was fed continuously through anAgilent 7890A gas chromatograph, where the sample loop was switched ontothe column every 35 min.

The sample was measured by the GC initially configured to AgilentConfiguration 7890-0047, which meets ASTM D3612A specifications, withmodified inlet temperature to avoid water condensation (150° C.) andlengthened total run time to avoid overlap with any present highermolecular weight hydrocarbons. This configuration uses an argonbackground with a flame ionization detector (FID) and a nickelmethanizing catalyst for the detection of hydrocarbons, CO₂, and CO, anda thermal conductivity detector (TCD) for the detection of H₂, O₂, N₂,and H₂O.

The results were calibrated using custom mixed gas calibrations providedby Airgas. Hydrogen was calibrated to 6.063% H₂ in argon, and 10 sampleshad a standard deviation of 0.051%. Carbon monoxide was calibrated to9.568% CO in N₂, and 10 samples had a standard deviation of 0.023%.Methane was calibrated to 20.000% CH₄ in N₂, and 10 samples had astandard deviation of 0.035%. CO₂, O₂, and N₂ were calibrated using dryair. Water was calibrated by using a target 1:1 ratio injected andvaporized in the reactor with air for 10 measurements with the total sumof products forced to 100%. This closed to a water amount of 47.85% witha standard deviation of 0.76% over 10 samples. Ethanol and acetaldehydewere calibrated by mixing with water to a known molar ratio andcalibrating by liquid injection of the diluted sample and comparison tothe water amount measured to avoid any homogeneous decomposition arisingfrom flow through the reactor. Sample amounts were calculated fromcalibrations by measuring the area of the peaks and comparing to theareas of peaks at the calibration composition.

Bar graphs showing product distribution and activity were made byscaling the product distribution such that the total height is the totalethanol conversion while the internal product distribution isrepresented by the relative size of each component. Error bars werecalculated by using the standard deviation of each scaled componentamount over the 36 measurements, scaled proportionally by the amounteach component is scaled. For each component, this error is estimated asσ_(A) ^(total)=√{square root over ((σ_(A) F)²+(σ_(F) A)²)}{square rootover ((σ_(A) F)²+(σ_(F) A)²)}where A is the fraction of total products for component A, σ_(A) is thestandard deviation in the fraction of total products for component Aover the 36 measurements, F is the total ethanol conversion percent, andσ_(F) is the standard deviation of the ethanol conversion percent overthe 36 measurements.

Homogeneous decomposition was measured by injecting a 1:10 ethanol/watermixture into the reactor with no catalyst present. At 300° C.,homogeneous decomposition showed 18.5% conversion of ethanol toacetaldehyde estimated as the ratio of measured acetaldehyde to the sumof the measured acetaldehyde and measured ethanol. Essentially no H₂ orCH₄ were measured. Catalysis is likely taking place in the tubing, whichcontains nickel, and on the stainless steel filter elements, so byplacing the catalyst powder as early as possible in the flow path,subsequent dehydrogenation is limited.

XRD crystallite sizes were determined by using the in situ furnaceattachment for the PANalytical X'Pert PRO diffractometer with theX'Celerator detector and a Cu Kα source. Spectra were analyzed usingJade software, and the peak width was used to calculate averagenanocrystallite size by fitting each peak to a Pearson-VII curve with noskewness.

TEM images were taken using a JEOL 2010 electron microscope at 200 keV.EDS was done using a GATAN detector in STEM mode on a JEOL 2010F with afield emission gun. BET data were collected using the Micromeritics ASAP2020, and pore size distributions were estimated by using MicromeriticsDFT Plus software with the original density functional theory model,with N₂ at 77 K on carbon with slit pores.

Overall conversion was calculated as the ratio of ethanol consumed toethanol injected, estimated using the amount of nitrogen detected as aninternal standard along with the known molar ratio of nitrogen toethanol at the inlet. The ratio of N₂ to ethanol at the inlet is 1.33:1based on the total flow rate of air and ethanol, so the conversion iscalculated as

${{conv}\mspace{14mu}\%} = {1 - \frac{\lbrack {{Et}{OH}} \rbrack}{\lbrack N_{2} \rbrack/1.33}}$where [EtOH] is the measured molar amount of ethanol in the outputstream and [N₂] is the measured molar amount of nitrogen in the outputstream.

Composition was calculated as the ratio of a given product to the totalsum of products including only CO₂, H₂, CO, CH₄, and acetaldehyde

${X\mspace{14mu}\%} = \frac{\lbrack X\rbrack}{\sum\limits_{i}\lbrack i\rbrack}$where X % is the calculated fraction for product X, and [X] is the molaramount of product X. The fractions were then scaled down byX%=X %×Conv %for easier display in a stacked bar chart. Water was consumed duringthis reaction, so the molar ratio of hydrogen to carbon could varydepending on the amount of steam reforming that occurred. Inexperiments, the actual measured H/C ratio varied quite a bit, from aslow as ˜3:1 at low temperatures to ˜6:1 at high temperatures.

Gas chromatography was used to take 36 samples over 21 h at temperaturesranging from 200 to 400° C. using 1000 mg of either M13-templated oruntemplated catalyst (˜12,000 h⁻¹ GHSV). In both cases, completeconversion occurred at 300° C. with approximately 60% H₂, less than 0.5%CO, and no acetaldehyde in the product distribution. The best results inliterature under similar conditions used Rh—Ni@CeO₂ and Co@CeO₂catalysts with 90%+ethanol conversion, but with 8-10% CO and 2-7%acetaldehyde in the product distribution, making the new catalystspreferable for use in fuel cells, where CO can act as a poison. See,e.g., Kugai, J.; et al. J. Catal. 2006, 238, 430-440; Kugai, J.; et al.Catal. Lett. 2005, 101, 255; and Llorca, J.; et al. J. Catal. 2002, 209,306-317, each of which is incorporated by reference in its entirety. Theuntemplated and M13-templated catalyst showed similar productdistributions under these conditions.

Increasing the GHSV from 12,000 to 36,000 h⁻¹ at 300° C. by decreasingthe amount of catalyst at the same input flow rate resulted in somedecrease in activity accompanied by more CO and acetaldehyde with lessCH₄, but ethanol conversion remained above 95%. Both catalysts showedsimilar product distributions. Samples without rhodium were also tested.In the nickel-only samples, the activity of the 10% Ni@CeO₂ catalyst wasparticularly notable in that nickel alone on CeO₂ achieved 100% ethanolconversion with an excellent product distribution, out performing themixed rhodium-nickel catalysts at 400° C. primarily due to the decreasein the amount of methane seen (8 to 2%) in the product distribution.Performance dropped off quickly as temperature was decreased,demonstrating that the rhodium was necessary for low temperatureconversion. Conversion over the nickel only catalyst was steady over 20h. The nickel-only catalyst performed more poorly when templated ontoM13 than when left untemplated. This decreased performance suggestedthat impurities remaining from the biological material werecontaminating the catalyst and reducing activity. For example, residualcarbon, sulfur, phosphorus, or other biologically common elements mayreduce the activity of the supported catalyst. This deactivation was notseen in the catalyst made with added rhodium.

In order to investigate the long-term thermal stability, catalysts werealso tested at 450° C. and 120,000 h⁻¹ GHSV by decreasing the amount ofcatalyst to 100 mg. Under these conditions, M13-templated catalystsshowed near complete conversion (99-100% ethanol conversion) and steadyperformance over 52 h with 70% H₂ and about 5% CH₄, 3% CO, and 1%acetaldehyde in the product stream. At similar flow rates andtemperatures, Rh—Ni@CeO₂ catalysts reported in literature showedcomplete conversion, but with 50% H₂ and 19% CH₄, while Co@CeO₂catalysts produced 70% H₂, 9% CO, and 2% acetaldehyde. See, e.g., Kugai,J.; et al. J. Catal. 2006, 238, 430-440; Kugai, J.; et al. Catal. Lett.2005, 101, 255; and Llorca, J.; et al. J. Catal. 2002, 209, 306-317;Wang, H. et al. Catal. Today 2007, 129, 305-312, each of which isincorporated by reference in its entirety.

M13-templated catalyst showed improved thermal stability compared tountemplated catalyst through a combination of resistance to surfacedeactivation on rhodium and less phase segregation. While M13-templatedcatalyst showed steady output over a 52 h measurement, untemplatedcatalyst showed decreased conversion over time, as shown in FIGS. 9A-9C((a) With M13 templating, total conversion dropped by only 1% over 52 h;(b) Untemplated catalyst showed total conversion dropping by 4% anddecreased hydrogen in the product fraction over 52 h. (c) Fasterdeactivation is seen in a second 52 h test of untemplated catalyst afterregeneration under air for 1 h, with total conversion dropping by 10%.).The decreased conversion was partially recovered by exposing thecatalyst to air for a short time, indicating a surface deactivation mostlikely caused by carbon buildup. However, a second 52 h measurement ofthe reactivated untemplated catalyst showed more rapid deactivation,indicating that the degradation of the catalyst was also caused bylong-term effects. Nanowires were not tested a second time as they didnot show noticeable deactivation over the first test.

XRD of the catalyst samples put on stream for stability tests showsthat, in both cases, impurity phases begin to appear (FIGS. 9D-9E; (d)XRD of M13-templated catalyst after 52 h on stream. Peaks for NiO,Rh₂O₃, and CeO₂ were seen. (e) XRD of untemplated catalyst after two 52h measurements with 1 h of regeneration under air. CeO₂ and NaCl peaksare seen, accompanied by Ni—Rh oxides. The double peak at 30° ischaracteristic of NiRh₂O₄.). In the case of M13-templated catalyst,small NiO and Rh₂O₃ peaks were seen after a 52 h measurement at 450° C.and 120,000 h⁻¹ GHSV. In the case of the untemplated sample, while NiOand Rh₂O₃ may be forming, a double peak at 30° suggested the formationof more complex mixed oxides such as NiRh₂O₄ after two 52 h measurementsat 450° C. and 120,000 h⁻¹ GHSV. On the basis of XRD peak broadening,the characteristic size of the NiO phases in the templated catalystafter 52 h on stream was ˜14 nm, while the Rh₂O₃ phases were ˜37 nm. Inthe untemplated sample after 105 h, the NiRh₂O₄ phase showed acharacteristic size of ˜52 nm. The more complex mixed nickel rhodiumoxide phase was not seen in the M13-templated catalyst, suggesting thatthe extent to which nickel oxide and rhodium oxides mixed to form mixednickel rhodium oxides may play a role in the permanent deactivation ofthe catalyst over time.

To determine what role chlorine played in the catalytic activity of thissystem, 1% Rh/10% Ni@CeO₂ was formed using cerium, rhodium, and nickelnitrate precursors. These particles performed poorly at 200° C. comparedto the particles synthesized from chloride precursors. While untemplated1% Rh/10% Ni@CeO₂ nanoparticles made from chloride precursors were stillfairly active at 200° C. with 73% ethanol conversion, 1% Rh/10% Ni@CeO2catalysts made from nitrates only showed 45% ethanol conversion. Thepoor performance of the catalysts made using only nitrates suggestedthat the chlorine ions are playing a role in the activity.

Other embodiments are within the scope of the following claims.

What is claimed is:
 1. A catalytic material, comprising a plurality ofcatalytically active nanoparticles formed together to provide a porouscatalytic material, the porous catalytic material having a BET surfacearea of greater than 150 m²/g.
 2. The catalytic material of claim 1,wherein the catalytically active nanoparticles comprise metal oxidenanoparticles.
 3. The catalytic material of claim 2, wherein the metaloxide comprises a manganese oxide, a magnesium oxide, an aluminum oxide,a silicon oxide, a zinc oxide, a copper oxide, a nickel oxide, a cobaltoxide, an iron oxide, a titanium oxide, yttrium oxide, a zirconiumoxide, a niobium oxide, a ruthenium oxide, a rhodium oxide, a palladiumoxide, a silver oxide, an indium oxide, a tin oxide, a lanthanum oxide,an iridium oxide, a platinum oxide, a gold oxide, a cerium oxide, aneodymium oxide, a praseodymium oxide, an erbium oxide, a dysprosiumoxide, a terbium oxide, a samarium oxide, a lutetium oxide, a gadoliniumoxide, a ytterbium oxide, a europium oxide, a holmium oxide, a scandiumoxide, or a combination thereof.
 4. The catalytic material of claim 1,wherein the catalytically active nanoparticles comprise a transitionmetal.
 5. The catalytic material of claim 1, wherein the catalyticallyactive nanoparticles comprise ceria.
 6. The catalytic material of claim5, wherein the catalytic material comprises thermal stability whereby ameasured x-ray diffraction pattern of the catalytic material issubstantially unchanged after 60 hours at 400° C.
 7. The catalyticmaterial of claim 1, comprising pores having a pore width of less than20 nm.
 8. The catalytic material of claim 1, wherein the catalyticmaterial is deposited on a support material.
 9. The catalytic materialof claim 8, wherein the support material comprises a ceramic supportmaterial.
 10. The catalytic material of claim 8, wherein the ceramicsupport material comprises a material selected from the group of silica,α-alumina, β-alumina, γ-alumina, rutile titania, austentite titania,ceria, zirconia, manganese oxide, manganese phosphate, manganesecarbonate, zinc oxide, or a combination thereof.
 11. The catalyticmaterial of claim 1, wherein the catalytically active nanoparticlescomprise a mixed metal oxide having the formula:M¹ _(i)M² _(j)O_(x) wherein i, j, and x are integers, and M¹ and M² areindependently selected from magnesium, aluminum, silicon, scandium,titanium, manganese, iron, cobalt, nickel, copper, zinc, yttrium,zirconium, niobium, ruthenium, rhodium, palladium, silver, indium, tin,lanthanum, cerium, praseodymium, neodymium, samarium, europium,gadolinium, terbium, dysprosium, holmium, erbium, ytterbium, lutetium,iridium, platinum, and gold.
 12. The catalytic material of claim 11,wherein the catalytic material is a nanowire.
 13. The catalytic materialof claim 1, wherein the catalytic material is a nanowire.